1. Field of the Invention
This invention relates to a bicycle, more particularly to a bicycle which is provided with a planetary-gear-train type transmission and an auxiliary electrical transmission that is driven automatically when a pedaling torque applied to the bicycle reaches a certain value, whereby the bicycle can be driven at a high speed in an energy-efficient manner.
2. Description of the Related Art
It is energy-consuming to run a bicycle at a high speed and to have a bicycle climb up a steep slope. A manually activatable electrical transmission is provided on a bicycle to solve this problem. However, the transmission is too bulky, and the load of a motor unit of the electrical transmission is too much, thereby shortening the serve life of the motor unit.